Re: [PATCH v11 1/4] random: add vgetrandom_alloc() syscall
From: Jann Horn <jannh@google.com>
Date: 2022-12-05 19:15:16
Also in:
linux-crypto, linux-patches, lkml
On Mon, Dec 5, 2022 at 3:01 AM Jason A. Donenfeld [off-list ref] wrote:
quoted hunk ↗ jump to hunk
+ mm->def_flags |= + /* + * Don't allow state to be written to swap, to preserve forward secrecy. + * This works in conjunction with MAP_LOCKED in do_mmap(), below, which + * actually does the locking (and associated permission check and accounting). + * Here, VM_LOCKONFAULT together with VM_NORESERVE simply make the mlocking + * happen the first time it's actually used, the same as when calling + * mlock2(MLOCK_ONFAULT) from userspace. + */ + VM_LOCKONFAULT | VM_NORESERVE |
Have you checked the interaction with this line in dup_mmap()? "tmp->vm_flags &= ~(VM_LOCKED | VM_LOCKONFAULT);" As the mlock.2 manpage says, "Memory locks are not inherited by a child created via fork(2)". I think the intention here is that the VMA should stay unswappable after fork(), right? Of course, trying to reserve more mlocked memory in fork() would also be problematic...